Interesting Algol 68 idiom: UPB a[@1]

[chris hermansen]

I think I'm missing something...

On Thu, Jan 15, 2026, 11:34 Jose E. Marchesi <jemarch@gnu.org> wrote:

>
> Hello people!
>
> Just wanted to share a nice idiom I learned while porting the ELLA
> sources.
>
> The usual way to iterated over the elements of a multiple with the
> intention of indexing them is:
>
>
>   for i from LWB a to UPB a do ... a[i] ... od
>
> This can be a bit cumbersome.  The following shorter version is not
> valid, because the lower bound of the multiple `a' may not be 1:
>
>   for i to UPB a do ... a[i] ... od
>
> This is also not correct, for the same reason:
>
>   for i to ELEMS a do ... a[i] ... od
>
> What I learned in ELLA is that you can do:
>
>   for i to UPB a[@1] do ... a[i] ... od
>

Doesn't that have to be

for i to UPB a[@1] do ... a[i + LWB a - 1] ... od

¿?



> It is short, and clear.
>
> I am actually tempted to put a fixed check in the compiler to compile it
> optimally so a trimmer doesn't get allocated.
>
> Hope this is useful.
> Salud!
>
Chris Hermansen · clhermansen "at" gmail "dot" com

C'est ma façon de parler.
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